Conventionally, a pipet device is often used in examining a liquid sample (such as blood or urine). A typical pipet device includes an elongate tube for sucking and retaining a liquid sample. Using such a pipet device, a taken sample is transferred from one container to another container or to an analyzer. (Hereinafter, this work is referred to as “pipetting”.)
In handling plural kinds of samples, different kinds of samples should not be mixed by pipetting. Conventionally, therefore, as shown in FIG. 5A, a disposable tip 9 is fitted outwardly to the end of a pipet nozzle 8 so that a sucked sample m does not come into contact with the pipet nozzle 8. When discharging of the sample m is finished, the tip 9 is replaced with a new tip.
However, the above-described prior art method is not sufficient to prevent different kinds of samples from mixing and has the following problems.
In discharging the sample m from the tip 9, it is difficult to completely let out the sample m, and a slight amount of sample m may remain on the inner surface of the tip 9. The remaining sample m may contaminate the pipet nozzle in the following manner. As shown in FIG. 5B, after the sample m is discharged, the tip 9 is pulled out from the pipet nozzle 8 in the arrow N1 direction for replacement. At that time, the volume of a space S within the tip 9 increases, generating a negative pressure in the tip 9. As a result, air flows into the tip 9 through an end opening 90a. The higher the speed in pulling out the tip 9 is, the larger negative pressure is generated in the tip 9, causing air to flow in at a higher speed. Such air flow transfers the sample m remaining in the tip 9 to the pipet nozzle 8, thereby contaminating the pipet nozzle 8.
Such a problem can be solved by making the tip 9 long or by pulling out the tip 9 at a low speed. However, if the former measure is taken, the volume of the tip 9 increases, which makes it difficult to suck the sample m precisely by a desired amount. Further, such an increase in length of the tip 9 leads to an increase in overall size of the pipet device. On the other hand, if the latter measure is taken, the replacement of the tip 9 requires much time, which deteriorates the work efficiency.